Hesitation free roller

ABSTRACT

A method and apparatus for rotating wafers in a scrubber, wherein both sides of a wafer are scrubbed without slipping or hesitating. A rotating roller imparts rotary motion to a semiconductor wafer during a cleaning process wherein both sides of a wafer are scrubbed. The rotating roller and wafer contact at their outer edges and the friction between their outer edges causes the wafer to rotate. The roller has an outer edge with a groove. The wafer edge is pinched inside the groove to create enough friction that when cleaning solutions are applied the wafer does not slip and continues to rotate. Also, the groove allows the roller to pinch the wafer just enough so that when the roller reaches the flat of the wafer, the roller may regain the radius of the wafer without hesitating.

This is a continuation of application Ser. No. 08/275,639, filed Jul.15, 1994, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor wafer processing,specifically the cleaning process of a semiconductor wafer.

2. Background Information

In the manufacture of semiconductor devices, the surface ofsemiconductor wafers must be cleaned of wafer contaminants. If notremoved, wafer contaminants may affect device performancecharacteristics and may cause device failure to occur at faster ratesthan usual.

One system used to remove wafer contaminants is called a scrubber,wherein both sides of a wafer are scrubbed. In this particular type ofscrubber a semiconductor wafer is scrubbed simultaneously on both sidesby brushes. Since the wafer is being scrubbed simultaneously on bothsides by the brushes there must be a way of holding the wafer in placeand rotating the wafer so the entire surface of the wafer is cleaned. Amechanism used for this purpose is called a roller.

The scrubber, wherein both sides of a wafer are scrubbed usuallycomprises a conveyor type mechanism, rollers, and brushes. In general,the wafer lies flat on the conveyor mechanism and the conveyor mechanismmoves the wafer into the brushes. While being scrubbed, the wafer issupported (or held horizontally) by the conveyor mechanism, brushes,rollers, or a combination thereof. As the wafer is being scrubbed by thebrushes the roller rotates the wafer so the entire wafer surface may becleaned. The roller itself is being rotated about its central axis by astepper motor. The rotary motion of the roller is then transferred tothe wafer when the edge of the roller comes into contact with the outeredge of the wafer.

FIG. 1 illustrates a prior art roller. The top and bottom surfaces 110and 120 of the roller are generally flat and the outer edge 130 of theroller has a slight concave indentation (concave outer edge). As isshown in FIG. 1, the concave outer edge of the roller contacts the outeredge of the wafer. When the roller and wafer contact each other,friction between the edges is created, so that the rotation of theroller causes the wafer to rotate. As can be seen from the Figure, thewafer and roller are in essentially single point contact.

One problem with the prior art roller is that the roller/wafer contactmay be insufficient, so that the wafer hesitates, i.e., fails to rotate.This problem is worsened when certain cleaning solutions are used, forexample ammonium hydroxide (NH₄ OH). The NH₄ OH or other cleaningsolution acts as a grease between the outer edge of the wafer and theouter edge of the roller, reducing the friction between the edges whenthey contact. Instead, the rotating roller continually slips off theedge of the wafer without imparting any motion to the wafer.

Another problem with the prior art roller is that the roller tends tostall (hesitate) when the roller is in the flat trying to regain theradius. FIG. 2 illustrates this problem. Most semiconductor wafers havea small portion of their outer edge which is flat, e.g. flat 251. Whenthe roller 200 reaches the point P on the flat 251 the wafer stalls(hesitates) until the roller is able to regain the radius. In otherwords the wafer hesitates until the roller can reach the curved portionof the outer edge of the wafer 250. This problem arises because theroller is downstream of the brush, such that the brush pushes the waferinto the roller. Therefore, when the flat first encounters the roller,it is pushed into it such that the roller can continue to rotate thewafer along the flat (so long as the above described slipping does notoccur). However, the prior art roller may not have enough of a grip topush the wafer back toward the brush to regain the radius.

If the wafer fails to rotate during the scrub operation, some areas ofthe wafer will not be scrubbed, so that the wafer is not cleaned to thelevel desired. An additional problem which may occur is that if thesystem relies on the roller to rotate the flat into a predeterminedposition for the next operation, the flat may be misplaced. For example,after the scrub operation, the wafer may next go to a spin dry operationwhere it is held by its edges. If the flat is misplaced, the wafer maynot be held properly.

What is needed is a method and apparatus for rotating the wafers in ascrubber, wherein both sides of a wafer are scrubbed without slipping orhesitating.

SUMMARY OF THE INVENTION

The present invention describes a method and apparatus for rotating asemiconductor wafer during the cleaning process in a scrubber, whereinboth sides of a wafer are scrubbed without slipping or hesitating. Inone embodiment, the apparatus comprises a roller having a groove whichpinches the substrate, thereby providing improved contact.

Additional features and benefits of the present invention will becomeapparent from the detailed description, figures, and claims set forthbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the accompanying figures in which:

FIG. 1 illustrates a side view of a prior art roller.

FIG. 2 illustrates a prior art roller at the point where stallingoccurs.

FIG. 3 illustrates the cleaning process of a wafer in a scrubber,wherein both sides of a wafer are scrubbed.

FIG. 4 illustrates a roller in a preferred embodiment of the presentinvention turning a semiconductor substrate having a first edge profile.

FIG. 5 illustrates a roller in a preferred embodiment of the presentinvention turning a semiconductor substrate having a second profile.

FIG. 6 illustrates the dimensions of a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION

A hesitation free roller is disclosed. In the following description,numerous specific details are set forth such as specific materials,configurations, dimensions, etc. in order to provide a thoroughunderstanding of the present invention. It will be obvious, however, toone skilled in the art that these specific details need not be employedto practice the present invention. In other instances, well knownmaterials or methods have not been described in detail in order to avoidunnecessarily obscuring the present invention.

FIG. 3 illustrates the cleaning process of a wafer in a scrubber,wherein both sides of a wafer are scrubbed (hereinafter "scrubber")which incorporates a preferred embodiment of the present invention.Although the present invention is described in conjunction with thescrubbing of a wafer, it will be appreciated that any similarly shaped,i.e. generally flat substrate, may be processed by the methods andapparatuses of the present invention. Further, it will appreciated thatreference to a wafer or substrate may include a bare or puresemiconductor substrate, with or without doping, a semiconductorsubstrate with epitaxial layers, a semiconductor substrate incorporatingone or more device layers at any stage of processing, other types ofsubstrates incorporating one or more semiconductor layers such assubstrates having semiconductor on insulator (SOI) devices, orsubstrates for processing other apparatuses and devices such as flatpanel displays, multichip modules, etc. The wafer 310 is placed betweenthe brushes 320 of the scrubber. Stepper motor 340 rotates the roller330 of the present invention. When the roller 330 is in contact with thewafer 310 friction is created between their edges. Thus, the rotatingmotion of the roller 330 and the friction that is created causes thewafer 310 to rotate. The rotation of the wafer 310 between the brushes320 allows the entire surface of the wafer to be cleaned. As can beseen, in a preferred embodiment, two rollers 330 contact the wafer attwo locations to rotate the wafer and to hold it in place (i.e., preventforward motion) as it is scrubbed.

FIG. 4 illustrates a roller 400 in a preferred embodiment of the presentinvention. The roller 400 comprises a somewhat flexible material. Ingeneral, the material of the roller should have a sufficient softnesssuch that the roller pinches the wafer's edge as described herein.Additionally, the material is preferably machinable, as it is desirableto avoid the high cost of tooling for molded rollers, and to avoid theparticle generation of parting lines. The material should not, however,generate excessive particles in use. Further, the material should have asufficient memory to retain its shape. In a preferred embodiment, aurethane, for example, 70 Durometer natural urethane is utilized. Thismaterial has been found to have sufficient softness, machinability,memory and low particle generation to meet the needs of the presentinvention. As shown, the top and bottom surfaces of roller 400 aregenerally flat. In a currently preferred embodiment, roller 400 has flatportions 401 and 402, slightly indented portions 404 and 403, and alsoan inner groove (groove) 410. When a wet wafer is being cleaned betweenthe brushes, it is pushed forward and inserted into the groove 410 ofroller 400, such that groove 410 pinches the wafer 450 causing increasedcontact, and therefore, increased friction on roller 400 and the edge ofwafer 450. Thus, when the roller 400 is rotated the friction causeswafer 450 to rotate. When cleaning solutions such as ammonium hydroxide(NH₄ OH) are used, the pinching of the wafer creates enough frictionthat the wafer 450 does not slip. Additionally, the pinching of thewafer squeezes the cleaning solution off of the edge, so that there isnot an excessive amount of solution in the contact area between theroller and the wafer's edge.

Also, when the hesitation free roller reaches the point P of the flat(as illustrated in FIG. 2) the pinching of the wafer creates enoughfriction on the edge of the wafer allowing the roller to regain theradius without stalling. In other words, the roller pinches the waferenough that it grips the edge of the wafer allowing the roller to reachthe curved portion of the wafer without hesitating.

FIG. 5 illustrates a wafer 550 in groove 410 of roller 330. As can beseen from the Figure, the edge profile of the wafer 550 is substantiallymore square than that of wafer 450. Because the roller 330 is made of aflexible material, groove 410 deforms slightly to fit the edge of wafer550, providing improved contact with it, as with wafer 450.

FIG. 6 illustrates the dimensions of a preferred embodiment of thepresent invention for use with a 6.0 inch (150 mm) wafer. It will beobvious to one of skill in the art that any of the dimensions may varydepending upon the wafer diameter and thickness and may be adjusted toserve the purpose of the present invention. The dimensions given belowfor roller 330 are merely an example of a preferred embodiment of thepresent example and are meant simply to illustrate, and not limit thescope of the present invention. As described herein, it is desired forthe groove to pinch the wafer or to some extent conform to the edge ofthe wafer. It is further desired that the pinching action does not occuron the upper or lower surface of the wafer. Therefore, the groove shouldhave a shape and dimension such that the wafer may not be inserted intoand gripped by contact between the groove wall and the upper and lowersurfaces of the wafer. In this regard, the "V" shape disclosed isadvantageous since as the edge enters the groove, it contacts the grooveat a narrow location of the groove while the surfaces of the wafer arenear or within a wider portion of the groove, thus avoiding contact.Further, the groove should not be too shallow such that the leading edgeof the wafer contacts the apex of the groove, prior to the walls of thegroove pinching the edges, thereby resulting in single point contact.

In a currently preferred embodiment, groove thickness 630 at the outeropening of the groove ranges from approximately 0.005-0.040 inch in acurrently preferred embodiment and, in general, is approximately equalto (e.g., within 25% of) the thickness of the wafer. For example, in oneembodiment groove thickness 630 is preferably tailored to beapproximately 0.005 inch greater than the thickness of the wafer. Thedistance between outer edge 640 and inner edge 650 is, in a preferredembodiment, approximately 0.067 inches. The distance 655 from the outeredge 640 to the center of curvature of the groove 410 is approximately0.620 inch a currently preferred embodiment. The maximum radius ofcurvature from this point is approximately 0.005 inch. In themanufacture of the roller 330, the roller is machined in a frozen state,as it is too flexible for machining otherwise. Since the portion of thebit which carves the groove 410 is relatively small, it will wear overtime. Therefore, initially the radius of curvature may be less than the0.005 inch specified above, as virtually all wafer edges will be grippedwithout penetrating any further. However, once the bit is worn down suchthat its radius of curvature is any greater than 0.005 inch, the bitshould be replaced so that subsequent rollers manufactured with a bitcontinue to grip all wafers. Groove angle 560, in a preferredembodiment, is approximately 24°.

Also in a currently preferred embodiment, roller thickness 610 isapproximately 0.433 inch. Roller length 620 is approximately 1.625inches. It should be noted that since the roller material is somewhatflexible the greater the surface thickness 670 the more rigid roller 330becomes. The surface thickness 670 may be varied to give desired degreeof flexibility in the groove and tightness of the pinch. A greatersurface thickness 670 leads to less flexibility, and therefore a tighterpinch. Conversely, a thinner surface thickness 670 leads to moreflexibility and a less tight pinch. Various thicknesses may be used toachieve the desired flexibility, for allowing the wafer to slip into thegroove 410, while still giving sufficient pinch. In a preferredembodiment the surface thickness 670 is approximately 0.062 inch.

It will be appreciated that many modifications of roller 330 may be madewithin the spirit and scope of the present invention. Referring to FIGS.4 and 5, note that the presence of the groove 410 provides for contactat at least two points, compared with the single point contact of theprior art roller 100. In this regard, it will be appreciated that the"point" of the contact is in reality a small area. It will further beappreciated that due to the pinching of the groove 410, each of the twopoints of contact of the present invention are generally larger areasthan the prior art single point contact. Thus, any shaped groove whichprovides this increased contact will achieve the objects of the presentinvention. For example, although a "V" shaped groove has beenillustrated, it will be appreciated that other shapes such as a "U"shaped groove, a substantially square groove, a groove with curvedwalls, etc., may be used. Further, it will be appreciated that thegroove need not be uniform. For example, the groove may have a wideangle at the opening, and a narrower angle farther in. In this regard,the roller may not have a discrete groove as such, but rather may have apinched "V" shape--e.g., a gradual and continuous transition from thesubstantially straight sidewall of the roller at the top and bottom tothe gripping, groove shaped section in the middle. Therefore, referenceherein to a groove is not meant to limit the invention to rollers havinga discrete, discernible groove but rather encompasses any roller havinga portion which pinches the edge of the wafer or conforms, at least tosome extent, to the edge of the wafer as described herein. If desired,the groove can be tailored to the edge profile of a specific type ofsubstrate. For example, the groove may have a portion which essentiallymates with the edge of the wafer. Typically, the portion which mateswith the edge is slightly smaller than the edge to provide bettercontact. However, wafer specific grooves have not been found to benecessary since, as described in conjunction with FIGS. 4 and 5, thesame groove 410 has been successful in rotating wafers having differentedge profiles. In general, the groove 410 has a thickness (dimension 630of FIG. 6) greater than the leading portion of the edge of the wafer, sothat the wafer edge readily fits into the groove 410. Additionally, thegroove narrows sufficiently (e.g., by having a maximum radius ofcurvature from a specified point, as in the embodiment described inrelation to FIG. 6) to pinch the wafer within the groove, withoutcontacting the top or bottom surfaces of the wafer.

Thus, a hesitation free roller has been described. Although specificembodiments, including specific equipment, parameters, methods, andmaterials have been described, various modifications to the disclosedembodiments will be apparent to one of ordinary skill in the art uponreading this disclosure. Therefore, it is to be understood that suchembodiments are merely illustrative of and not restrictive on the broadinvention and that this invention is not limited to the specificembodiments shown and described.

What is claimed is:
 1. A system for processing a semiconductor substratecomprising:a double sided scrubber, wherein said double sided scrubberincludes a roller to rotate said semiconductor substrate, said rollerhavingan outer wall, and; a v-shaped groove, said v-shaped groove beingperpendicular to a central axis of rotation and in a circular positionsubstantially around the circumference of said outer wall of saidroller, said v-shaped groove having a v-shape operable to pinch an edgeof said semiconductor substrate when said roller contacts the edge ofsaid semiconductor substrate, wherein said roller rotates and positionssaid semiconductor substrate such that both sides of the semiconductormay be scrubbed in said double sided scrubber.
 2. The system asdescribed in claim 1 wherein said v-shaped groove contacts said edge ofsaid substrate on at least two points.
 3. The system as described inclaim 1 wherein said v-shaped groove has an opening in the range ofapproximately 0.005-0.040 inch.
 4. The system as described in claim 1wherein said roller comprises a flexible material.
 5. The system asdescribed in claim 4 wherein said flexible material comprises urethane.6. The system as described in claim 5 wherein said urethane comprises 70Durometer natural urethane.
 7. A system for processing a semiconductorsubstrate comprising:a double sided scrubber, wherein said double sidedscrubber includes a roller to rotate said substrate, said rollerhavingan outer wall; a v-shaped groove in said outer wall, said v-shapedgroove having an opening in the range of approximately 0.005-0.040 inchwith a v-shape operable to pinch an edge of said semiconductor substratewhen said roller contacts the edge of said semiconductor substrate; anda central axis.
 8. The system as described in claim 7 wherein saidroller comprises a flexible material.
 9. The system as described inclaim 8 wherein said flexible material comprises urethane.
 10. Thesystem as described in claim 9 wherein said urethane comprises 70Durometer natural urethane.
 11. A system for processing a semiconductorsubstrate comprising:a double sided scrubber, wherein said double sidedscrubber includes a roller to rotate said semiconductor substrate, saidroller havinga central axis; a top portion; a bottom portion; an outerwall; and a v-shaped groove, said v-shaped groove being in a positionsubstantially around said outer wall of said roller and substantiallybetween said top portion and said bottom portion of said roller, saidv-shaped groove having a thickness of approximately 0.005-0.040 inch atthe outer opening of said groove, and a depth of approximately 0.067inch, and wherein said v-shaped groove has a v-shape operable to pinchan edge of said semiconductor substrate when said roller contacts theedge of said semiconductor substrate.
 12. The system as described inclaim 11 wherein said top portion comprises a top flat portion and a topindented portion and said bottom portion comprises a bottom flat portionand a bottom indented portion.
 13. The system as described in claim 11wherein said top flat portion and said bottom flat portion havethicknesses of approximately 0.062 inch.
 14. The system as described inclaim 11 wherein said roller has a thickness of approximately 0.433inch.
 15. The system as described in claim 11 wherein said roller has adiameter of approximately 1.625 inches.
 16. The system as described inclaim 11 wherein said roller comprises a flexible material.
 17. Thesystem as described in claim 16 wherein said flexible material comprisesurethane.
 18. The system as described in claim 17 wherein said urethanecomprises 70 Durometer natural urethane.
 19. The system as described inclaim 11 wherein said v-shaped groove further comprises a groove angleof approximately 24°.
 20. An apparatus for use in a semiconductorfabrication system comprising:a roller, said roller for rotating asemiconductor substrate in a double sided scrubber, said roller havinganouter wall, and; a v-shaped groove, said v-shaped groove beingperpendicular to a central axis of rotation and in a circular positionsubstantially around the circumference of said outer wall of saidroller, said v-shaped groove having a v-shape operable to pinch an edgeof said semiconductor substrate when said roller contacts the edge ofsaid semiconductor substrate.
 21. The apparatus as described in claim 20wherein said groove contacts said edge of said substrate on at least twopoints.
 22. The apparatus as described in claim 20 wherein said groovehas an opening in the range of approximately 0.005-0.040 inch.
 23. Theapparatus as described in claim 20 wherein said roller comprises aflexible material.
 24. The apparatus as described in claim 23 whereinsaid flexible material comprises urethane.
 25. The apparatus asdescribed in claim 24 wherein said urethane comprises 70 Durometernatural urethane.
 26. An apparatus for use in a semiconductorfabrication system comprising:a roller, said roller for rotating asemiconductor substrate in a double sided scrubber, said roller havinganouter wall; a v-shaped groove in said outer wall, said v-shaped groovehaving an opening in the range of approximately 0.005-0.040 inch with av-shape operable to pinch an edge of said semiconductor substrate whensaid roller contacts the edge of said semiconductor substrate; and acentral axis.
 27. The apparatus as described in claim 26 wherein saidroller comprises a flexible material.
 28. The apparatus as described inclaim 27 wherein said flexible material comprises urethane.
 29. Theapparatus as described in claim 28 wherein said urethane comprises 70Durometer natural urethane.
 30. An apparatus for rotating a substrate ina semiconductor fabrication system comprising:a roller, said roller forrotating a semiconductor substrate in a double sided scrubber, saidroller havinga central axis; a top portion; a bottom portion; an outerwall; and a v-shaped groove, said v-shaped groove being in a positionsubstantially around said outer wall of said roller and substantiallybetween said top portion and said bottom portion of said roller, saidv-shaped groove having a thickness of approximately 0.005-0.040 inch atthe outer opening of said groove, and a depth of approximately 0.067inch, and wherein said v-shaped groove has a v-shape operable to pinchan edge of said semiconductor substrate when said roller contacts theedge of said semiconductor substrate.
 31. The apparatus as described inclaim 30 wherein said top portion comprises a top flat portion and a topindented portion and said bottom portion comprises a bottom flat portionand a bottom indented portion.
 32. The apparatus as described in claim30 wherein said top flat portion and said bottom flat portion havethicknesses of approximately 0.062 inch.
 33. The apparatus as describedin claim 30 wherein said roller has a thickness of approximately 0.433inch.
 34. The apparatus as described in claim 30 wherein said roller hasa diameter of approximately 1.625 inches.
 35. The apparatus as describedin claim 30 wherein said roller comprises a flexible material.
 36. Theapparatus as described in claim 35 wherein said flexible materialcomprises urethane.
 37. The apparatus as described in claim 36 whereinsaid urethane comprises 70 Durometer natural urethane.
 38. The apparatusas described in claim 30 wherein said v-shaped groove further comprisesa groove angle of approximately 24°.